diff --git a/src/utils/__tests__/cssDimensions.test.js b/src/utils/__tests__/cssDimensions.test.ts
similarity index 96%
rename from src/utils/__tests__/cssDimensions.test.js
rename to src/utils/__tests__/cssDimensions.test.ts
index 2deb302..fa4ac56 100644
--- a/src/utils/__tests__/cssDimensions.test.js
+++ b/src/utils/__tests__/cssDimensions.test.ts
@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import { ensureUnit } from '../cssDimensions';
+import { ensureUnit, type RawDimension } from '../cssDimensions';
 import { describe, expect, test } from 'vitest';
 
 describe('cssDimensions', () => {
@@ -129,7 +129,13 @@ describe('cssDimensions', () => {
         },
     ])(
         'ensureUnit returns $expected with input $dimension',
-        ({ dimension, expected }) => {
+        ({
+            dimension,
+            expected,
+        }: {
+            dimension: RawDimension;
+            expected: string;
+        }) => {
             expect(ensureUnit(dimension)).toBe(expected);
         },
     );
diff --git a/src/utils/cssDimensions.js b/src/utils/cssDimensions.ts
similarity index 77%
rename from src/utils/cssDimensions.js
rename to src/utils/cssDimensions.ts
index c0e35d7..2010aab 100644
--- a/src/utils/cssDimensions.js
+++ b/src/utils/cssDimensions.ts
@@ -14,7 +14,13 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-export const ensureUnit = function ensureUnit(d) {
+/*
+ * null and undefined because they are intended to represent empty input
+ * values
+ */
+export type RawDimension = null | number | string | undefined;
+
+export const ensureUnit = function ensureUnit(d: RawDimension): string {
     if (!d) d = 0;
 
     // ensure that it is a string